Polymeric roof sheeting is often used as single-ply roofing membrane for covering industrial and commercial flat roofs. Such membranes are typically applied to the roof surface in a vulcanized or cured state.
Because of outstanding weathering resistance and flexibility, cured EPDM based roof sheeting has rapidly gained acceptance as an effective barrier to prevent the penetration of moisture through the roof being covered. While this material is suitable for covering the roof, and although it is capable of withstanding most traffic, it is customary to apply walkway pads, comprising other rubber or polymeric materials, directly onto the membrane defining a traffic pattern to areas of the roof to which travel is required. Typically, it is common to specify the use of walkway pads in areas where the frequency of traffic exceeds one excursion per month.
Presently, such walkway pads are typically made from various scrap rubber or claimed rubber materials such as recycled tires, or uncured workaway or uncured off-specification rubber compounds available from tire manufacturing facilities or various other industrial facilities which have various off-specification mechanical rubber goods available for use. These rubber compositions generally include such rubber materials as natural rubber, synthetic polyisoprene, styrene butadiene rubber (SBR), polybutadiene, butyl rubber (IIR) or the like or mixtures and blends thereof. Still other walkway pads have been produced from polymeric materials such as neoprene, polyvinyl chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene and other similar olefin-type polymers.
Walkway pads are generally about 30 inches square and about 0.3 inches thick, although thicknesses generally range between about 0.25 and 0.5 inches. The pad provides upper and lower surfaces. The lower surface is generally relatively smooth while the upper surface may be textured in order to improve traction.
Walkway pads are currently applied to roofing membranes and other forms of roof covering material with the use of liquid adhesives or tape adhesives which are applied to the walkway pad prior to installing the walkway pad on the roof surface. This method typically involves cleaning and/or priming the walkway pad and then applying the liquid or adhesive tape to the pad, although alternative methods, such as set forth in U.S. Ser. No. 08/606,119 owned by the Assignee of record, are being explored. The applied adhesive, which is oftentimes used in the form of a seam tape which itself may include EPDM or EPM, keeps the walkway pad in place on the roof surface, and the walkway pad serves to protect the roof system, especially the membrane from foot traffic.
While various walkway pad compositions are known, the art has not heretofore recognized the benefit of a walkway pad composition containing 100 percent ethylene-propylene copolymers and terpolymers as the polymeric material used in the walkway pad composition. Such a walkway pad would certainly be compatible with the necessary adhesive tapes typically used to adhere the walkway pad to a roofing membrane, especially where the roofing membrane composition includes EPDM as its base polymer. Given the rapid acceptance of EPDM as the base rubber component in many roofing membranes today, the use of a similar EPDM as the sole polymer, or as the major component (with a minor amount of EPM) in a walkway pad composition would also appear desirable. Moreover, given the excellent weathering characteristics of EPDM, such an EPDM walkway pad composition would appear to provide a significant improvement in the art over current walkway pad compositions containing various other rubber or polymeric materials such as natural rubber, synthetic polyisoprene, styrene butadiene rubber (SBR), polybutadiene, butyl rubber (IIR) or the like or mixtures and blends thereof, as well as those compositions containing polymeric materials such as neoprene, polyvinyl chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene and other similar olefin-type polymers.
Walkway pads should also meet standard physical property requirements. For instance, a preferred walkway pad should show no signs of cracking or splitting when folded around a one-inch bending radius at 40.degree. F. The walkway pad should lay flat and remain flexible at temperatures as low as -20.degree. C. Still further, the pad should be free of any mold release on the non-dimpled or textured side. Additional desirable physical properties include an elongation of at least 100 percent using ASTM-D-412; a brittleness temperature of at least -40.degree. C. according to ASTM-D-2137; and a Shore "A" Hardness of between about 55 to 70 as tested in accordance with ASTM-D-2240.
Thus, the need exists for a walkway pad composition which has excellent low temperature and heat aging properties as well as superior weathering resistance as compared to other walkway pad compositions which include other polymeric components such as natural rubber, synthetic polyisoprene, styrene-butadiene rubber (SBR), polybutadiene, and butyl (IR) rubber. The walkway pads should also meet the physical performance requirements desired of walkway pad compositions. Desirably, such a fully compounded EPDM walkway pad composition would have a Mooney viscosity ranging between about 45 and about 60 Mooney units (ML/4 at 100.degree. C.), and an elongation at break of at least 100 and, more preferably, at least 250 percent.